Limnology of Lago Loiza, Puerto Rico

The principal chemical, physical and biological characteristics of Lago Loize, P.R., and its main tributaries were studied from 1973-74. The lake supplies an average of 300,000 cubic meters per day of water to metropolitan San Juan. Flows from Rio Grande de Loize and Rio Gurabo contribute 84.0 percent of the water, 67.3 percent of the nitrogen, and 66.8 percent of the phosphorus to the lake. About 31 percent of the nitrogen and 45 percent of the phosphorus were retained in the lake, which has a mean flusing rate of 19 times per year. The lake 's capacity declines at a rate of about 1.9 percent per year and is about 14.9 million cubic meters. Sewage inputs to the lake 's tributaries average 18,560 cubic meters per day. Fecal coliform bacteria in numbers ranging from 100 to 6,700,000 were recorded throughout the tributaries and the lake. In the lake, dissolved oxygen concentration is less than 5.0 milligrams per liter below the 1.5-meter depth. Lago Loize is a hypereutrophic lake, with an average total nitrogen concentration of 1.7 milligrams per liter and 0.33 milligram per liter of total phosphorus. (USGS)